419 Dive Log Australasia AUGUST 2026

A male Southern Blue-ringed Octopus climbs a sponge covered pylon in pursuit of his mating partner.

span that can reach around 20 cm in fully grown individuals. Compared with some of the larger local octopuses of Port Phillip Bay, such as the M ā ori Octopus (Macroctopus maorum) and the Pale Octopus (Octopus pallidus), it is tiny. But size is misleading. This animal carries one of the most powerful defensive systems of any creature in the bay. Its venom contains tetrodotoxin, a potent neurotoxin that can block nerve signals and cause paralysis. In serious cases, the greatest danger is respiratory failure, which can be fatal without immediate breathing support. There is no antivenom for a blue-ringed octopus bite. Survival depends on immediate and continuous artificial respiration, including CPR and rescue breathing, until the body naturally metabolises the neurotoxin. That sounds frightening, and it is serious, but the risk needs to be understood properly. Bites are rare and usually occur when the animal is handled, trapped, picked up or otherwise disturbed.

The safest rule is simple: admire it, photograph it and leave it alone. Like many of Port Phillip Bay’s most interesting small predators, the Southern Blue-ringed Octopus is mainly nocturnal. During the day, it usually stays tucked away and out of sight. At night, it becomes more active and easier to spot, not only because it is out hunting, but also because torchlight makes it easier to pick out its shape and colours among rubble and sand. Feeding mainly on crustaceans, especially small crabs, it is a compact and highly precise hunter, built for quick, efficient ambushes rather than brute force. Its strike is fast and controlled. The octopus can grab a crab, pierce it, inject venom and then feed on the softened tissues. This is where the blue-ringed octopus becomes far more interesting than its reputation. Its toxic saliva is not only a defence against potential predators; it is also a crucial part of how this animal hunts and feeds.

55

Dive Log Australasia #419 August‘26

www.divelog.net.au